The present invention relates to a process for producing a fluid bed palladium-promoted catalyst useful in the production of vinyl acetate from ethylene, acetic acid and oxygen-containing gas. In addition, the present invention relates to a novel fluid bed support and process of using the support for the manufacture of palladium-promoted fluid bed catalyst used in the manufacture of vinyl acetate.
The production of vinyl acetate by reacting ethylene, acetic acid and oxygen together in the gas phase in the presence of a catalyst is known. Typically, the catalysts are in fixed bed form and supported on a porous carrier material such as silica or alumina.
Early examples of these catalysts show that palladium and gold are distributed more or less uniformly throughout the carrier (see, for example, U.S. Pat. Nos. 3,275,680, 3,743,607 and 3,950,400 and Great Britain Patent No. 1,333,449 and South African Patent No. 687,990). Subsequently, it was recognized that this was a disadvantage since it was found that the material on the inner part of the carrier did not contribute to the reaction since the reactants did not significantly diffuse into the carrier. To overcome this problem, new methods of catalyst manufacture were devised with the aim of producing catalyst in which the active components were concentrated on the outer-most shell of the support. For example, Great Britain Patent No. 1,500,167 claims catalyst in which at least ninety percent of the palladium and gold is distributed in that part of the carrier particle which is not more than thirty percent of the particle radius from the surface. In addition, Great Britain Patent No. 1,283,737 teaches that the degree of penetration into the porous carrier can be controlled by pre-treating the porous carrier with an alkaline solution of, for example, sodium carbonate or sodium hydroxide. Another approach which has been found to produce particularly active catalyst is described in U.S. Pat. No. 4,048,096 and other methods of producing shell-impregnated catalyst are disclosed in U.S. Pat. Nos. 4,087,622 and 5,185,308. Each of these patents is primarily concerned with the manufacture of fixed bed catalyst useful for the manufacture of vinyl acetate. However, U.S. Pat. No. 3,950,400 also discloses that the catalyst disclosed therein may be used in a fluid bed reactor. In addition, Great Britain Patent No. 1,266,623 allegedly discloses a fluid bed catalyst for vinyl acetate manufacture which comprises palladium promoted with various alkali, alkaline earth or other metals.
It would be economically beneficial if the manufacture of vinyl acetate could be performed in a fluid bed process as well as a fixed bed process. Some of the typical benefits from a fluid bed process would be that the fluid bed reactor design is simpler than a multi-tubular fixed bed reactor, increased catalyst life is to be expected because no deactivation would take place due to hot spots which are typical of a fixed bed reactor, continuous addition of make-up catalyst can maintain peak performance and virtually eliminate catalyst change-outs, and higher production rates can be expected because substantially higher oxygen levels may be safely fed into the reactor without producing a flammable mixture.
Until the discovery of the process of the present invention, the preparation of palladium-promoted catalyst in fluid bed form has not led to catalyst having the necessary properties leading to a viable economical fluid bed process for the manufacture of vinyl acetate. The process of the present invention overcomes the problems associated with the prior art resulting in a catalyst giving high performance and adequate attrition resistance so that it may be used in the manufacture of vinyl acetate.
It is the primary object of the present invention to provide a process for the manufacture of a fluid bed palladium-metal-promoted alkali metal catalyst useful in the manufacture of vinyl acetate.
It is another object of the present invention to provide a novel support for use in the production of a fluid bed palladium-metal-alkali-metal-promoted catalyst useful in the fluid bed manufacture of vinyl acetate.
It is still another object of the present invention to provide a novel process for the production of a support useful in the manufacture of vinyl acetate catalyst.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing objects of the present invention, the process of manufacturing a fluid bed vinyl acetate catalyst characterized by the following formula comprising Pdxe2x80x94Mxe2x80x94A wherein M equals barium, cadmium, gold, lanthanum, niobium, cerium, zinc, lead, calcium, strontium, antimony, or mixtures thereof; and A equals at least one alkali metal or mixture thereof comprises impregnating a pre-formed microspheroidal support wherein at least 50% of the particles have a particle size diameter selected to be below 105 microns with a solution comprising a metal salt of the palladium, M and at least one alkali metal and drying the impregnated catalyst. The substantially inert particulate support typically comprises microspheroidal particles selected from the group consisting of alumina, silica, titania, zirconia, and/or mixtures thereof.
In another embodiment of the present invention the process is performed using an aqueous solution free or substantially free of any organic solvent.
In a preferred embodiment of the present invention the metal salt of the alkali metal is separately impregnated onto the support, preferably subsequent to the impregnation of the solution comprising the salts of palladium and M element onto the support material.
In another embodiment of the present invention, the impregnated support may be subjected to known reduction procedures (e.g., heating under reducing conditions) to form a deposit of palladium and M on the surface of the support. The reduction can take place either before or after the deposition of the alkali metal solution.
In a still further preferred embodiment of the present invention the catalyst is dried at a temperature below 80xc2x0 C, preferably between about 60xc2x0 to 70xc2x0 C.
In another preferred embodiment of the present invention the particle size(particle diameter) of the substantially inert support material is selected such that at least 50% of the particles are below about 105 microns. Preferably, at least 75% of the particles are below 105 microns, especially preferred being at least 85% below 105 microns. Finally the preferred support is substantially free of sodium.
In another embodiment of the present invention, the support for the manufacture of the vinyl acetate catalyst comprises a mixture of substantially inert microspheroidal particles having a pore volume of between 0.2 to 0.7 cc/g and/or a surface area of between 50 to 200 m2/g and at least 50% of said particle are less than 105 microns.
In a preferred aspect of this embodiment of the present invention, at least 75% of the particles are below 105 microns, especially preferred being at least 85% below 105 microns. 76
In another embodiment of the present invention, the support for the manufacture of the vinyl acetate catalyst comprises microspheroidal inert particles, preferably silica, zirconia, alumina, titania or mixtures thereof wherein said particles have a pore volume of between 0.2 to 0.7 cc/g and/or a surface area of between 50 to 200 m2/g and are obtained from a mixture of less than 100% to 20% inert support sol and greater than zero percent to 80% dried inert particles.
In a preferred embodiment of this aspect of the present invention, the pore volume of the inert particles is between 0.3 to 0.65 cc/g, especially preferred being 0.4 cc to 0.55 cc/g.
In a further preferred embodiment of this aspect of the present invention, the surface area is between 50 to 150 m2/g, especially preferred being 60 to 125 m2/g.
In a further aspect of this embodiment of the present invention, the silica microspheroidal support material is manufactured by mixing between 20% to less than 100% silica sol with 80% to greater than zero percent silica such as Aerosil(copyright), spray drying said mixture at an elevated temperature of between 115xc2x0 to 280xc2x0 C., preferably 130xc2x0 to 240xc2x0 C., and calcining said spray dried particles preferably at a temperature of between 550xc2x0 to 700xc2x0 C., preferably between 630xc2x0 to 660xc2x0 to form the support material.
Typically, the weight percent of the palladium, M and alkaline in the catalyst of the present invention are: 0.1 to 5.0 wt % palladium, preferably 0.2 to 4.0 wt %; greater than 0 to 10 wt % alkali metal, preferably 0.1 to 8.0 wt %, most preferably 0.1 to 5.0 wt %; greater than 0 to about 5.0 wt % M, preferably 0.1 to about 4.0 wt %.
The catalysts of the present invention may be used in a fluid bed reactor for the reaction of ethylene with oxygen to produce vinyl acetate. The reaction temperature is suitably 100xc2x0 to 250xc2x0 C., preferably 135xc2x0 to 190xc2x0 C. The reaction pressure is suitably 50 to 200 psig, preferably 75 to 150 psig.